Pumping is an example of a method typically used to fill compressed gas cylinders with compressed gasses. According to such a method, a gas material is typically pumped in liquid form through a heat exchanger using a cryogenic pump. The heat exchanger converts the liquid into gas form by increasing the material's temperature. The gas then exits the heat exchanger and is transferred into compressed gas cylinders.
One drawback to conventional methods results from the fact that many liquefied gases, such as helium, may be expensive and difficult to maintain, due for example, to vaporization and resultant pressure changes over time. Further, pumping liquefied helium is impractical, therefore a gas booster pump is used.
Pumping liquefied helium with a cryogenic pump also presents challenges. According to conventional methods, a pneumatic gas booster pump must be used to pump helium in order to achieve a higher ultimate pressure than the pressure supplied. However, pneumatic gas booster pumps are slow and require large air compressors to run. These large air compressors are expensive, often being valued many times above the cost of the pump itself. Furthermore, such systems typically generate a great deal of wasted energy and in turn heat, often utilizing exhaust air to cool the pump, as the heat of compression of the pumped gas can result in temperatures in excess of 200° F. if left uncooled.